1. Field of the Invention
The present invention relates generally to batteries of the multi-cell lead acid type and more particularly to a system which eliminates the rigid case employed in prior battery systems. Still more specifically the present invention relates to batteries in which battery elements are encapsulated in an acid-resistant, self-curing liquid such as a rubber or resin.
2. Description of the Prior Art
In the manufacture of batteries of the SLI variety, such as those employed with automotive electrical systems, it is well-known to employ a thermoplastic case surrounding the individual battery elements. The elements are typically combined by welds, soldering or straps to provide the desired voltage, with the casing providing containment for the electrolyte employed with the system. The individual elements frequently include a plurality of positive plates and negative plates with intermediate separators. Numerous prior art devices disclose such systems. In most systems used today, a cover, which may include suitable venting systems, is employed to provide for battery maintenance and for relief of gaseous pressures that may be generated in the harsh environment of a lead-acid battery.
There has been a recognized need for many years to reduce the weight of battery components, especially those used in automotive applications and the like, and the heavy thermoplastic containers used with present battery systems contribute to the problem Moreover, with different automobile models and for different size batteries, numerous molds must be made for preparing the containers. Prototype development proceeds slowly for this reason. Moreover, shipping of the containers is costly because of the amount of air transported with the thermoplastic casings (which do not fully nest), and warehouse floor space is taxed by large stacks of empty storage containers. It would be highly desirable to be able to prepare batteries without using the conventional thermoplastic containers, especially if a system could be developed which would allow prototypes to be developed more rapidly and which would eliminate shipping costs and permit processing of the batteries using other components in the manufacturing system which are presently in place.
The idea of surrounding battery components with plastic film is itself known in the art as illustrated by U.S. Pat. No. 4,530,153 issued Jul. 23, 1985 to Pierson for "Manufacturing Recombination Electric Storage Cells". In this patent, a recombination storage cell is prepared by pasting positive and negative electrode grids with damp electrode material and forming a cell pack of alternating positive and negative materials interleaved with separators. The cell pack is inserted into a plastic bag while the active electrode material is still damp and the electrodes are dried within the bag by subjecting them to temperatures in excess of 25.degree. C. The cell pack is then inserted into a typical battery container.
Small lead storage batteries which are enclosed in plastic film are also disclosed in U.S. Pat. No. 4,664,994 issued May 12, 1987 to Koike, et al. for "Enclosed Lead Storage Battery And Process For Producing The Same". In this patent, a plate assembly comprising a positive and negative plate with an intermediate separator is surrounded by a jacket made of film- or sheet-formed synthetic resin. The film is a multi-layer laminate and a system is disclosed for permitting the terminals of the electrode to be sealed to the film. A venting technique is also disclosed. The patent does not disclose combining elements to form batteries of the type involved in the present invention. In the preferred embodiment of the Koike, et al. patent, a heat sealable polyolefin film is provided on the facing surfaces of the film laminate.
Another system for preparing a lead-acid battery is disclosed in U.S. Pat. No. 4,758,482 issued Jul. 19, 1988 to Yamana, et al. entitled "Enclosed Type Lead Batteries And Method For Producing The Same". In this device, a plate stack having its ears connected to terminals contained in a synthetic resin cap is surrounded by an enclosure formed of film or sheet synthetic resin. The film is thermally fused at the peripheral edge of its opening to the cap. Completed elements, according to the inventors, can be placed into a case thereby resulting in some reduction in the cost of manufacturing high performance enclosed lead-acid batteries.
Several patents exist in the battery art which describe processes for dipping various battery components in certain materials. See, for example, U.S. Pat. No. 4,524,509 issued Jun. 25, 1985 to Wegner for "Enveloping A Battery Plate By Dip Process And Product Produced Thereby" (dipping a plate to provide a microporous battery separator material thereon) and U.S. Pat. No. 4,885,007 issued Dec. 5, 1989 to Wegner for "Dip Process For Enveloping A Battery Plate" (also forming a separator envelope about a battery plate).
A system for preparing battery elements and completed batteries which avoids certain fabrication problems with prior art systems and results in battery elements with reduced weight would be a significant advance in the art.